C++ STL映射一键二值

Question

I have a situation where I have a map with one key and two values ex.

std::map<std::string, std::pair<double, double> > myMultiValueMap

depending on a condition I need to either update one value or the other.

I'd am looking for syntax to insert/ find the key and update either values in this map

yes I have used the insert on Maps before, but was not sure on multivalue map

std::map<std::string,double> myMap;
myMap.insert(std::make_pair("12345",0.00));

and find and update too

std::map<std::string,double>::iterator it =  myMap.find(("12345");

Answer 1

std::map requires two template arguments, one key and one value type. But it is up to you to use arbitrary type for "value".

struct TestValue {
    int Value1;
    int Value2;
    int Value3;
    TestValue(int v1, int v2, int v3) : Value1(v1), Value2(v2), Value3(v3) {}
};

std::map<std::string, TestValue> myMap;
myMap["test"] = TestValue(1, 2, 3);

Answer 2

Inserting an item into the map:

myMultiValueMap[strKey] = make_pair(firstDouble, secondDouble);

Checking if an item exists:

if( myMultiValueMap.find(strKey) != myMultiValueMap.end() ) {
    // Item Exists
}

Updating an item:

myMultiValueMap[strKey].first = newFirstDouble;
myMultiValueMap[strKey].second = newSecondDouble;

You should use this for these to work

using namespace std;

Please take time and read the examples from cplusplus.com

Answer 3

I like bkausbk's answer and would have commented on the answer but don't have rep. Map sometimes has a problem with needing a default constructor. I know this from another SO post . I got it to work by setting default arguments (the post has other solutions)

So I changed the constructor in bkausbk's answer to:

TestValue(int v1 = 0, int v2 = 0, int v3 = 0) : Value1(v1), Value2(v2), Value3(v3) {}